In recent years, for securing energy resources of the future, various countries of the world are studying about a variety of energy sources that can be obtained easily from the natural to make use of the energy sources, and some developed countries in energy utilization including South Korea take advantage of the variety of energy sources as the main auxiliary power generation system for the power supply in their countries.
Energy sources available for an energy renewal may include (solar) light, heat, vibration source as well as an RF energy source, etc. Among them, the RF source utilizes the fact that radio waves from base stations or repeaters are propagated over space for wireless communication and its application is limited because of having a power per unit area of about 0.1 μW/cm2, which is extremely very low 1/1,000 to 1/10,000 times as compared to other energy sources. In the case of a sensor that is one of representative applications utilizing an energy renewal, its power consumption becomes at most 50 μW˜50 mW and, therefore, its utility decreases in RF energy renewal techniques.
Further, as the efficiency of a rectenna depends on the magnitude of the RF energy received, the lower the reception power is, the efficiency of a receiver circuit is rapidly decreases, and the larger the fluctuation of the received power is, the insufficient amount of energy becomes charged. In spite of that, the amount of RF energy that is being propagated into the atmosphere for the purpose of mobile communications is considerable as compared to the harvestable amount of power per unit area. Therefore, if a beneficial technology is developed to use the RF energy as a renewable energy source not to render the RF energy to be extinguished naturally, its value is inexhaustible.
On the other hand, a high-power RF energy source may be antennas of repeaters, base stations or the like in our daily lives. However, a technique for utilizing the RF energy was nothing but the collection of energy radiated from the repeaters and the base stations using rectennas disposed adjacent to the antennas. In such a case, it is possible to design the rectennas to have the frequency similar to the resonant frequency in order to increase the collection amount of energy by the rectennas. However, it has a problem that energy generated originally from an existing antenna is deflected in a direction where a rectenna is disposed due to a strong mutual coupling between the antenna and the rectenna to deteriorate the performance of the antenna, which results in fading the original purpose of the renewable energy.
Therefore, there are needs to provide a technology for renewing RF energy efficiently without impairing the intrinsic performance of the existing antenna and a technology for utilizing to renew the radiation component which is wasted unnecessarily from a high-power energy source with a relatively high power density when renewing the RF energy.